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ADS131E08: ADS131 E and M synchronization compatibility

Simon Tartakovsky
Prodigy 20 points
Part Number: ADS131E08
Other Parts Discussed in Thread: ADS131M08,

Tool/software:

Hi all,

I am developing a modular data acquisition system for cryogenic temperature devices. This system currently is based around the ADS131m08 ADCs which appear to be a very cost effective way to achieve the performance I need. However, the E family of chips offers a few features that I would benefit from greatly - 2.5V reference support and high input impedance at unity gain.

I am considering switching a subset of the ADCs to the E family however as the system is modular I would require both of these to work "together". Working together just means sharing a clock and being synchronized. 

I see that the E08 has a much stricter clock requirement (2Mhz) which the M08 chip will accept. The M08 chip is synchronized by pulsing the SYNC/RESET pin low for a few clock periods while the E08 has a START pin which the datasheet indicates can be used by multiple ADCs to sync them.

My question is as follows: can I tie the START pin of a ADS131E08 to the SYNC/RESET pin of the ADS131M08 and sync all devices by generating a short low pulse to sync all devices? The low state will sync the M08 devices and my understanding of the E08 datasheet implies that the rising edge will sync the E08 devices. The timing requirements of the E08 do not explicitly state the minimum pulse duration for a START condition to occur.

Thank you all for your advice!

Bonus question: The M08 has ESD protection which means that with a large enough series resistor the inputs of the device are not damaged if my input circuitry rails for some reason, does the E08 have these as well?

  • +1
    TI__Guru 54136 points

    Hi Simon Tartakovsky,

    To answer your main question, yes you can start both ADS131E08 and ADS131M08 using their respective pins. However, the actual settling times are different between the devices, so I am not sure how this will be useful unless you synchronize the devices before every capture. Also, the interface timing requirements are different between these ADCs, as are the commands, so it would be difficult to communicate with them on a shared bus for example. Finally, the E08 is looking for a positive edge on START while the M08 is looking for a negative edge on SYNC/RESET. Therefore, you would need an inverter on one of these pins to get them to start at the same time, but I don't think they will be synchronized at any point thereafter

     And yes, the ADS131E08 has ESD diodes on the input pins. Also note that the ADS131M0x devices only have ESD diodes to AVDD, not AVSS i.e. they only clamp to the positive rail, not the negative rail. This is described in section 8.3.1 in the ADS131M08 datasheet

    -Bryan

  • 0 in reply to Bryan Lizon86
    Prodigy 20 points

    Thank you Bryan, this indeed answers my question.

    with respect to input protection: the ADS131M0x device section 8.3.1 states that negative analog input is protected by the reverse breakdown voltage. In practice thus far the part has been exceptionally robust to the driving circuitry railing the inputs under and above the supply rails through a series resistor.  As long as I stay within the 10mA quoted in the absolute maximums in the datasheet is there any reason to worry?

    -Simon

  • +1 in reply to Simon Tartakovsky
    TI__Guru 54136 points

    Hi Simon Tartakovsky,

    Yes this is correct with respect to the ESD cells on the M0x pins

    You generally want to be <<10mA to provide plenty of margin on the pins. In other words, don't operate at 9.9mA all the time because this will stress the silicon even though it is technically within the absolute maximum ratings

    -Bryan